This invention relates generally to means for sealing clearance space between a rotary shaft and a member surrounding the shaft, and more particularly to a sealing assembly of the "air-purge" type, that is, the type utilizing the flow of a gas under pressure to effect the sealing action.
This invention is especially directed to a sealing assembly for sealing the clearance space between the drive shaft of a mixer, for example, and the surrounding wall through which the shaft extends so as to prevent escape through the clearance space of material being mixed by the mixer. Sealing of this clearance space presents a particularly difficult problem when the material being mixed is relatively fine-grain and fluent, such as a powdered sugar mix or a cake frosting mix. Seals heretofore used to prevent escape of this material from the mixer have been largely ineffective, primarily because the powdery material has tended to work its way into the sealing area where it quickly abrades the sealing elements with consequent loss of effective sealing action. As a result, it has been necessary either to replace the sealing elements at frequent intervals at high cost, or suffer escape of material from the mixer.
Reference may be made to U.S. Pat. Nos. 3,887,199, 4,021,050 and 4,153,259 for sealing devices of the air-purge type.